Parenteral administration of pyrophosphate for prevention or treatment of phosphate or pyrophosphate depletion

ABSTRACT

Phosphate depletion, a physiological condition commonly seen in certain patient populations, including alcoholics, malnourished, acutely ill patients, patients receiving parenteral nutrition, patients being re-fed after prolonged fasting, and dialysis patients, requires intravenous supplementation when oral repletion is not feasible. This invention provides a method and pharmaceutical composition for therapeutic administration of pyrophosphate, instead of phosphate, for phosphate or pyrophosphate repletion. During hemodialysis or peritoneal dialysis significant removal of phosphate and pyrophosphate occurs. Pyrophosphate depletion predisposes patients to vascular calcification. This invention further provides a method and pharmaceutical composition for therapeutic administration of pyrophosphate for phosphate or pyrophosphate repletion by addition of pyrophosphate to hemodialysis or peritoneal dialysis solutions.

CROSS-REFERENCE TO RELATED APPLICATIONS

Applicant claims benefit of the Provisional Application entitled“Parenteral Administration of Pyrophosphate For Prevention Or TreatmentOf Phosphate Or Pyrophosphate Depletion” that was filed on Dec. 30, 2003and has Application No. 60/481,840.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH & DEVELOPMENT

No Federally sponsored research & development was used in making thisinvention.

FIELD OF THE INVENTION

The present invention relates to a method and composition for treatmentof phosphate or pyrophosphate depletion in a mammal.

BACKGROUND

Phosphate depletion is commonly seen in certain patient populationsincluding alcoholics, malnourished, acutely ill patients, patientsreceiving parenteral nutrition, patients being re-fed after prolongedfasting, or dialysis patients. Oral repletion of phosphate may not befeasible if the patient is not able to eat, suffers from malabsorptionor has continuing losses of phosphate that cannot be adequately treatedby the oral route. In such clinical situations phosphate is commonlyadministered intravenously. This invention provides a method andpharmaceutical composition for administering pyrophosphate for theprevention or treatment of phosphate or pyrophosphate depletion.

Specifically, in patients with kidney failure, excess removal ofphosphate and pyrophosphate anions can occur during hemodialysis orperitoneal dialysis. Depletion of these anions from tissues and plasmaleads to disorders of bone and mineral metabolism including osteomalaciaand calcification of soft tissues and bone disease.

Kidneys are integral to maintenance of normal bone and mineralmetabolism including excretion of phosphate. Patients with kidneyfailure are unable to appropriately regulate serum mineral balance andtend to retain phosphate that is absorbed from the various dietarycomponents. A high serum level of phosphate is associated with excessivesecretion of parathyroid hormone and a tendency to calcification of thesoft tissues including the blood vessels.

In dialysis patients, hyperphosphatemia is controlled by removal ofphosphate during hemodialysis or peritoneal dialysis. Peritonealdialysis is a continuous process during which a transfer of phosphatesfrom the blood compartment to the peritoneal fluid occurs relativelyefficiently. However, the usual three times a week hemodialysis is notable to remove all the phosphates absorbed and generated during theinter-dialytic interval. Therefore, the majority of patients on theusual three times a week hemodialysis are prescribed agents such ascalcium acetate that bind dietary phosphate in the gut, therebydecreasing the absorption of dietary phosphate. It has been shown thatincreasing the efficiency of dialysis can improve general well-being andoverall health of the patient, while preventing complications of kidneyfailure.

Conventional Hemodialysis (CHD), delivered thrice weekly, results inlarge biochemical and body fluid volume fluctuations with potentiallyhazardous peaks and troughs, is still highly unphysiologic. Morefrequent dialysis schedules may better mimic the normal physiologicalsituation. These include short daily home hemodialysis (SDHD) and slowlong-hours nocturnal hemodialysis (NHD) performed 6-10 hours nightly 6-7times per week. The considerable clinical improvements when patientschange to SDHD and NHD dialysis have been almost uniformly observed, andinclude better well-being and energy, better nutritional indices, higherhemoglobin, better blood-pressure control, much improved intra-dialysistolerance with fewer cramps, hypotension, nausea, headaches, lesser postdialysis symptoms including fatigue, cramps and lightheadedness. Theminor effect of short daily dialysis on phosphate removal-in contrast tothe major effect of daily nocturnal dialysis, with its long, 8 hoursessions-probably is related to the complex phosphate kinetics duringand after dialysis. After the start of a dialysis session, serumphosphate decreases rapidly to low, though further constant, serumconcentrations, only to rise at the end of a 4-hour session. This rapiddecrease is caused by an effective phosphate clearance through thedialyzer in the beginning. Thereafter, phosphate starts to betransferred to the blood from extravascular compartment, possibly bone,during the course of a dialysis session, probably due to an activemechanism, triggered by the fall in serum phosphate. Thisinter-compartmental transfer of phosphate prevents a further decrease inserum phosphate. However, it also determines the rate of phosphateremoval during the course of a dialysis session, independent from thetype of dialyzer or PTH level. This inter-compartmental transfer canlead to tissue depletion of phosphate.

However, large amounts of phosphate, matching daily intake, can only beremoved through long sessions, as in the case of nocturnal hemodialysis.The creation of more “starting periods” with high initial removal ratesthrough frequent dialysis sessions appear to be less effective. The massbalance studies by Al-Hejaili et al. have showed that phosphate removalby NHD (43.5±20.7 mmol) was significantly (P<0.05) higher than by SDHD(24.2±13.9 mmol) but not by CHD (34.0±8.7 mmol) on a per-treatment basis(Al-Hejaili et al. 2003). With the increased frequency of treatmentsprovided by quotidian dialysis, the weekly phosphorus removal(261.2±124.2 mmol) by NHD was significantly higher than by SDHD(P=0.014) and CHD (P=0.03). The highly effective removal of phosphatewith NHD not only allows the discontinuation of phosphate binders but infact, in some patients phosphate has to be added to the dialysate in aconcentration of 0.5-4.5 mg/dl in order to prevent the development ofhypophosphatemia. In the London Daily/Nocturnal Hemodialysis Study,after being on NHD for a period of 10 months, 2 of the 11 patientsneeded phosphate supplementation in the dialysate to prevent thedevelopment of hypophosphatemia (Lindsay et al. 2003). Furthermore,patients on NHD experience negative calcium balance with increasingserum levels of parathyroid hormone and bone-specific alkalinephosphatase, when a dialysate calcium concentration is 1.25 mmol/L.Hence, dialysate calcium concentration has to be increased to 1.75mmol/L in NHD patients (Lindsay et al. 2003). Patients have likewiserequired phosphate supplementation in other studies of NHD. (Lockridgeet al. 2001).

In NHD patients requiring phosphate supplementation via the dialysate,as the blood passes through the dialyzer, phosphate is infusedconcurrently with calcium and bicarbonate since the concentrations ofcalcium and bicarbonate in the dialysate in NHD patients are 1.5-2.25mmol/L and 28-35 mEq/L respectively. At the same time, inhibitors ofcalcification such as pyrophosphate (PPi) and citrate are dialyzed out.This chemical imbalance in the post-dialyzer blood compartment, beforeit has equilibrated with rest of the blood compartment, is characterizedby high calcium and phosphate levels in the presence of an alkaline pH,a microenvironment that is highly conducive to precipitation of calciumin the vessel wall. As this blood enters the heart and bathes the heartvalves and the myocardium, there is an increased risk of calcificationof the heart valves and the myocardium. The blood is then pumped by theheart into the major vessels and onto the smaller vessels therebypredisposing to calcification of the arterial tree.

A significant proportion of hemodialysis patients have subnormal serumlevels of PPi. Serum PPi was below normal (<40 pg/dl) in about 40% ofpatients with normal serum alkaline phosphatase (n=42) and in about 60%of patients with elevated serum alkaline phosphatase (n=40) (David etal. 1973). Pyrophosphate deficiency may be a risk factor for depositionof calcium into the small vessels of the skin causing an inflammatoryvasculitis called calciphylaxis that can lead to gangrene of the skinand underlying tissues, resulting in severe, chronic pain. Calciphylaxismay necessitate amputation of the affected limb and is commonly fatal.There is currently no effective treatment for this condition. Ectopiccalcification, if left untreated, results in increased morbidity anddeath.

Thus, there exists a need for an effective method of maintainingadequate plasma concentrations of calcification inhibitors andinhibiting ectopic calcification in patients with kidney failureundergoing hemodialysis or peritoneal dialysis. The present invention,by administering to the dialysis patient a therapeutic amount of apyrophosphate via the dialysate satisfies this need and provides relatedadvantages as well.

SUMMARY OF THE INVENTION

The present invention provides a method for replenishing plasmaphosphate and/or pyrophosphate in a subject comprising administeringinto the subject's circulation a therapeutically effective amount of apyrophosphate. The therapeutically effective amount of a pyrophosphateis most effectively administered intravenously. In preferred embodimentsof the present invention, the therapeutically effective amount of apyrophosphate is administered intravenously by a slow, continuousinfusion into the subject, during hemodialysis using an extracorporealcircuit, or during peritoneal dialysis.

It is a further object of this invention to provide a method forreplenishing plasma phosphate and/or pyrophosphate in a subjectcomprising administering a therapeutically effective amount of apyrophosphate to a subject wherein the pyrophosphate is pyrophosphoricacid or an inorganic or organic salt thereof and the therapeuticallyeffective amount of the pyrophosphate is from about 0.05 micromoles(μmol) to about 45 millimoles (mmol) of pyrophosphate per day, amountsthat are equivalent to the amounts of phosphate that are removed duringdialysis of a subject.

Yet another object of this invention is to provide a method of preparinga composition for replenishing plasma phosphate and/or pyrophosphate ina subject comprising adding a therapeutically effective amount of apyrophosphate to a dialysis solution that is to be used to dialyze thesubject or to a hemodialysis concentrate. In a preferred embodiment ofthe present invention, the pyrophosphate is added to a bicarbonateconcentrate that is used in the preparation of a hemodialysis solution.

These objects have been achieved by providing liquid or solidcompositions for replenishing phosphate and/or pyrophosphate in asubject's plasma comprising a pyrophosphate. The pyrophosphate ispyrophosphoric acid or an inorganic or organic salt thereof and thecomposition is suitable for addition to a peritoneal dialysate, ahemodialysis solution or a concentrate that is used in the preparationof a hemodialysis solution, most preferably a bicarbonate concentrate.The dialysate composition used to dialyze the patient contains apyrophosphate in a concentration equivalent to an inorganic phosphorusconcentration of 0.5-4.5 mg per deciliter.

In a preferred embodiment of the present invention, a liquid or solidhemodialysis concentrate composition for replenishing phosphate and/orpyrophosphate in a subject's plasma is provided, wherein thepyrophosphate is pyrophosphoric acid or an inorganic or organic saltthereof. In other preferred embodiments of the present invention, aconcentrate composition is provided wherein the concentrate compositionhas a 30- to 50-fold higher pyrophosphate concentration than the finaldesired concentration of pyrophosphate in the hemodialysate used todialyze the patient.

Upon further examination of the specification and appended claims,further objects and advantages of the invention will become apparent tothose skilled in the art.

DETAILED DESCRIPTION OF THE INVENTION

This invention provides a method to supply phosphate to a subject inneed of replenishing the phosphate and/or pyrophosphate in the subject'splasma via a dialysate that contains inorganic phosphorus (Pi) in theform of pyrophosphate (which contains a P—O—P linkage), which is brokendown in the body to phosphate by the action of pyrophosphatases such asalkaline phosphatase. Since pyrophosphate (PPi) is an anti-calcificagent, it is able to supplement phosphate without the added risk ofcalcification. In fact, it may prevent calcification, since the risk ofcalcification is highly increased in dialysis patients.

The dialysate concentration of pyrophosphate may be determined by thepatient's plasma phosphate level. A concentration of 0.5-4.5 mg ofinorganic phosphorus (Pi) has to be added per deciliter of dialysate inorder to prevent hypophosphatemia. This concentration of can be achievedby addition of a suitable, bio-available salt of pyrophosphate (PPi)such as sodium (Na₄P₂O₇ or Na₂H₂P₂O₇), potassium, calcium or magnesiumpyrophosphate or as pyrophosphoric acid (H₄O₇P₂, contains 35% Pi byweight).

Pyrophosphoric acid and its salts are soluble in water. The solubilityof pyrophosphoric acid at room temperature is about 700 g/100 ml ofwater. The addition of PPi to the acid hemodialysis concentrate resultsin formation of a precipitate. Therefore, PPi is not compatible with theacid concentrate that is used to prepare hemodialysis solutions. On theother hand, pyrophosphoric acid and pyrophosphate salts are freelysoluble in the bicarbonate concentrate that is used to preparehemodialysis solutions. Therefore, it is feasible to achieve requisitelevels of PPi in the dialysate by addition of 30-50 fold higher levelsto the bicarbonate concentrate. Similarly, PPi can be added toperitoneal dialysis solutions that are used by patients on peritonealdialysis in order to prevent phosphate depletion and/or preventcalcification.

PPi is readily dialyzable across hemodialysis membranes since themolecular weight of pyrophosphate anion is only about 175 Dalton. Theclearance or dialysance of PPi exceeds that of creatinine using a coilkidney. Consequently, there is a rapid decline in serum PPi duringdialysis. When PPi is added to the dialysate in a concentration thatexceeds the PPi concentration in the plasma, there is rapid transferfrom the dialysate to the blood compartment. The dialysance of PPi bymodern high efficiency or high flux dialyzer membranes has not beenreported but is expected to be highly efficient.

Pyrophosphate (PPi) is known to be a potent inhibitor of calcification.PPi is used as anti-scaling additives in washing powders, water and oilbrines to prevent calcium carbonate scales. Furthermore, it is one ofthe main anti-tartar agents in toothpastes world-wide. Therefore, it isreasonable to expect that dialysate solutions comprising pyrophosphatemay help preserve the hollow fiber hemodialysis membranes, therebyprolonging the life of membranes and increasing reuse.

The role of pyrophosphate in inhibition of calcification has beenstudied extensively in vitro and in human and animal studies (Fleisch etal. 1965). PPi in a concentration as low as 0.1 μM can bind strongly tocrystals of hydroxyapatite, thereby inhibiting further precipitation ofcalcium phosphate. The normal concentration of PPi in human plasma of2-4 μm/L is within the range at which a strong inhibition of calciumphosphate precipitation is observed in vitro even in the presence ofnucleating substances, such as collagen. PPi at a 2 μm/L concentrationis rapidly and almost completely taken up by the apatite crystals. Therapidity of the binding reaction suggests that PPi binds predominantlyto the surface of apatite crystals. PPi is present mainly in the highratio shell and/or the surface layer of the crystals where it displacesorthophosphate. Electron microscopy and x-ray diffraction analysis haveshown that there is no increase in crystals size when PPi coats theapatite crystals even from solutions highly super saturated with calciumand phosphate. The inhibition of calcification by PPi has been explainedas a blockage of crystal growth centers by adsorption of the compoundonto the apatite crystals at sites of calcification. Fleisch andco-workers have reported that PPi inhibits calcification in aortas andkidneys of rats treated with large amount of vitamin D₃ (Fleisch et al.1965). Therefore, plasma PPi is critical in preventing precipitation.

In dialysis patients, a therapeutically effective amount ofpyrophosphate anions, either as an acid or a functional salt thereof,can be administered either intravenously either by slow continuousintravenous infusion or via the hemodialysis or peritoneal dialysissolution. The method consists of administering a therapeuticallyeffective amount of pyrophosphate, thereby replenishing plasma phosphateand/or pyrophosphate levels. Furthermore, an effective amount ofpyrophosphate is added to the dialysis solution used to dialyze the saidhemodialysis or peritoneal dialysis patient, thereby effectivelyreplenishing plasma phosphate and/or pyrophosphate levels.

The therapeutic level of PPi in the dialysate may vary from μM to mMrange, depending on the following factors

-   -   1. Patient related factors including serum PPi and Pi levels,        body weight, presence or absence of calcification, and other        bone and mineral parameters such as bone alkaline phosphatase        and parathyroid hormone levels,    -   2. Modality of dialysis: hemodialysis versus peritoneal        dialysis, duration of dialysis (conventional versus daily versus        slow nocturnal, CAPD versus CCPD), dialysis vintage.    -   3. Clinical indication: treatment versus prevention of        hypo-phosphatemia versus hypo-pyrophosphatemia, prevention        versus treatment of vascular calcification, severity of vascular        calcification (asymptomatic vs. calciphylaxis/gangrene).        References:

Al-Hejaili F, Kortas C, Leitch R, et al. Nocturnal but not short hoursquotidian hemodialysis requires an elevated dialysate calciumconcentration. J Am Soc Nephrol 2003; 14 (9):2322-8.

David D S, Sakai S, Granda J, et al. Role of pyrophosphate in renalosteodystrophy. Transactions—American Society for Artificial InternalOrgans 1973; 19:440-5.

Fleisch H, Schibler D, Maerki J, et al. Inhibition of aorticcalcification by means of pyrophosphate and polyphosphates. Nature 1965;207 (3):1300-1.

Lindsay R M, Alhejaili F, Nesrallah G, et al. Calcium and phosphatebalance with quotidian hemodialysis. Am J Kidney Dis 2003; 42 (1Suppl):24-9.

Lockridge R S, Jr., Spencer M, Craft V, et al. Nocturnal homehemodialysis in North America. Adv Ren Replace Ther 2001; 8 (4):250-6.

1. A method for the replenishment of plasma phosphate in a subject inneed thereof, said method comprising parenterally administering directlyto the subject in need of replenishment of plasma phosphate a liquidcomposition comprising a compound selected from the group consisting ofpyrophosphoric acid, an organic pyrophosphate, calcium pyrophosphate,magnesium pyrophosphate, sodium pyrophosphate, and potassiumpyrophosphate in an amount that is therapeutically effective for thereplenishment of plasma phosphate, said compound being in the directlyadministered composition at a concentration equivalent to an inorganicphosphorus concentration in the range of 0.5 to 4.5 mg per deciliter. 2.The method of claim 1 wherein the compound is administeredintravenously.
 3. The method of claim 2 wherein the compound isadministered intravenously by a slow, continuous infusion into thesubject.
 4. The method of claim 1 wherein the composition is ahemodialysis solution and the compound is administered to a subjectduring hemodialysis by inclusion of the compound in the hemodialysissolution used to hemodialyze the subject.
 5. The method of claim 4wherein the hemodialysis solution has been prepared by adding thecompound to a bicarbonate concentrate which was used to make thehemodialysis solution.
 6. The method of claim 1 wherein the compositionis a peritoneal dialysis and the compound is administered to theperitoneal cavity of a subject during peritoneal dialysis by inclusionof the compound in a peritoneal dialysis solution used to dialyze thesubject.